SOYBEAN BOWMAN-BIRK PROTEASE INHIBITOR IS A HIGHLY EFFECTIVE INHIBITOR OF HUMAN MAST-CELL CHYMASE

Soybean Bowman-Birk protease inhibitor (BBI) is an inhibitor of serine proteases with two functional inhibitory domains of different specifi cities: one is specific for chymotrypsin-like proteases, the other for trypsin-like proteases, Chymase and tryptase are serine proteases whi ch are stored in mast cell granules and released upon degranulation. T his work investigated the inhibition of human chymase and tryptase by BBI. Active-site titration of human skin chymase by BBI demonstrated t hat BBI was a highly effective inhibitor of human chymase, Virtually s toichiometric inhibition of chymase by BBI was observed at 1.0 nM chym ase, Kinetic studies of the inhibition reaction yielded an association rate constant of 4.0 x 10(5) M-1 s(-1) and a dissociation rate consta nt of 1.7 x 10(-5) s(-1). From these two constants we estimate a K-i o f 50 pM. Chymase/BBI complexes did not dissociate in SDS-PAGE analyses under nonreducing conditions, consistent with the formation of a very tight complex with little tendency to dissociate. In contrast to chym ase, human tryptase was not inhibited by BBI. These studies demonstrat e that BBI is a good inhibitor of human chymase, exhibiting reaction p roperties better than physiological inhibitors described to date. (C) 1997 Academic Press.